---
title: Microservice Design Principles
summary: Core design principles and best practices for creating well-structured microservices at FlowMart
sidebar:
    label: Design Principles
    order: 2
---

At FlowMart, we follow a set of design principles that guide the creation of new microservices. These principles help ensure our services are maintainable, scalable, and aligned with our overall architectural vision.

## 1. Domain-Driven Design

Each microservice should be aligned with a specific business domain or subdomain. We follow Domain-Driven Design (DDD) principles to identify service boundaries:

### Bounded Contexts

- Define clear bounded contexts for each service
- Maintain a separate ubiquitous language within each context
- Document domain models and context maps

### Example Domains at FlowMart

| Domain | Description | Example Services |
|--------|-------------|------------------|
| Order | Order processing and management | order-service, order-history-service |
| Inventory | Product inventory management | inventory-service, stock-management-service |
| Customer | Customer accounts and profiles | customer-service, authentication-service |
| Payment | Payment processing and refunds | payment-service, refund-service |
| Shipping | Shipping and logistics | shipping-service, tracking-service |
| Catalog | Product information management | product-service, search-service |

## 2. Single Responsibility

Each microservice should have a single responsibility and a clear purpose:

- **Focus on one business capability**: Services should do one thing well
- **Right-sized services**: Not too large (mini-monolith) or too small (nano-service)
- **Cohesive functionality**: Related functions should be grouped together

## 3. Data Ownership

Microservices should own their data and maintain data autonomy:

- Each service has its own database or data store
- No direct data sharing between services
- Data is exposed through well-defined APIs
- Services should be the single source of truth for their domain data

## 4. API Design

All FlowMart microservices must follow our [API Management and Governance Strategy](/docs/architecture-records/drafts/03-api-management-governance):

### RESTful APIs

- Use consistent resource naming conventions
- Follow standard HTTP methods and status codes
- Implement proper error handling and validation
- Design for backward compatibility

### Event-Driven Interfaces

- Define clear event schemas using AsyncAPI
- Document event ownership and responsibilities
- Follow event versioning standards
- Implement idempotent event consumers

## 5. Resilience and Fault Tolerance

Microservices must be designed to handle failures gracefully:

- Implement circuit breakers for downstream dependencies
- Use timeouts and retries with exponential backoff
- Design for graceful degradation of functionality
- Implement health checks and readiness probes

## 6. Observability

All services must expose monitoring and observability data:

- Structured logging (using our ELK stack)
- Metrics exposure (Prometheus format)
- Distributed tracing support (Jaeger)
- Health check endpoints

## 7. Security by Design

Security must be integrated into every service:

- Authentication using OAuth 2.0 / OpenID Connect
- Authorization using role-based access control
- TLS encryption for all communications
- Input validation and output encoding
- No sensitive data in logs or traces

## 8. Testability

Services should be designed with testing in mind:

- High unit test coverage (minimum 80%)
- Integration tests for all critical paths
- Contract tests for API interfaces
- Easy local testing setup
- Simulated dependencies for development

## 9. Configuration Management

Services should follow our configuration management approach:

- Environment-specific configuration via Kubernetes ConfigMaps
- Secrets management via HashiCorp Vault
- Feature flags for conditional functionality
- No hardcoded configuration values

## 10. Independence and Deployability

Services should be independently deployable:

- No deployment coupling with other services
- Infrastructure as Code for all resources
- Self-contained CI/CD pipelines
- Blue/green or canary deployment capabilities

## Microservice Checklist

Use this checklist when designing a new service:

- [ ] Service aligns with a specific business domain
- [ ] Clear bounded context defined
- [ ] Service owns its data
- [ ] APIs follow company standards
- [ ] Event schemas are documented
- [ ] Resilience patterns implemented
- [ ] Observability instrumentation added
- [ ] Security controls integrated
- [ ] Comprehensive test suite created
- [ ] Configuration externalized
- [ ] Independent deployment pipeline configured

## Next Steps

- Learn how to [create a Node.js microservice](/docs/guides/creating-new-microservices/node-service)
- Explore [TypeScript service implementation](/docs/guides/creating-new-microservices/typescript-service)
- Understand our [Terraform infrastructure modules](/docs/guides/creating-new-microservices/terraform-modules) 